On almost every North American freight train, an end-of-train (EOT) device, also known as EOTD, ETD, or FRED (flashing rear-end device), has now replaced a caboose to perform various important functions. The EOT device is typically mounted on the back of the last car and includes a battery-operated tail-light as well as electronic equipment for other safety-related functions. For example, one significant function of an EOT device is to monitor the brake-pipe pressure. A sensor may extend from the EOT device and attach to the end of an air hose to gather data on the brake-line pressure, which is one of the most crucial measurements on any train. The brake-line pressure information is transmitted by radio messages from the EOT device to the engine cab, which may be equipped with a head-of-train (HOT) device to receive, decode, and display the data. Thus, a train engineer or driver can monitor the integrity of the brake line as he sets and releases the brakes. By receiving instructions from the HOT device via radio transmissions, the EOT device may also assist in emergency braking when necessary. EOT devices may be further equipped with motion sensors or positioning capabilities to determine the motion and/or location of the rear end of a train. For example, many EOT devices now include GPS (the Global Positioning System) receivers that pinpoint their own coordinates. Via radio transmissions, an EOT device can inform the engine cab (i.e., the corresponding HOT device) if the rear end of the train is stopped or moving forward or backward. Radio messages from the EOT device to the HOT device may also include other information such as the ON/OFF status of the red tail-light and its battery charge state.
It can be appreciated from the above introduction that it is critically important for an HOT device and an EOT device on a train to function and to communicate with each other properly. Indeed, railway regulations mandate proper two-way communications between HOT and EOT devices. Prior to the operation of a train, a pair of HOT and EOT devices should be matched up through an arming procedure. Currently, every EOT device is configured to only respond to a matched HOT device and to ignore messages received from all other EOT devices and non-matched HOT devices.
On a given freight train, the HOT and EOT devices exchange messages on a pair of radio channels (duplex), that is, with the LOT device transmitting on a first channel and listening on a second channel and with the HOT device transmitting on the second channel and listening on the first channel. For example, EOT devices may transmit on 457.9375 MHz and receive on 452.9375 MHz, while HOT devices may transmit on 452.9375 MHz and receive on 457.9375 MHz. According to some implementation, message duration of EOT and HOT devices is about 150 ms. A message from an HOT device is supposed to elicit a response from a matched EOT device, which response should start within 18 ms of the end of the HOT message.
In reality, however, EOT and HOT devices do not always operate as intended. Railroads have always had some level of trouble with EOT and HOT equipment. Before a train departs, a user may experience problem linking an HOT device with a corresponding EOT device, whereupon a new device is often attempted, followed by another device, until successful linking is achieved and the train departs. An HOT or EOT device found defective on one train in some cases may somehow work effectively on another shorter train. During train operations, communications between a pair of EOT and HOT devices can still become spotty or non-existent as a result of power failure, hardware malfunction, and/or software errors.
It is therefore desirable to test HOT and EOT devices in order to reduce their failure rate during train operations. A number of testers have been developed for HOT and LOT devices. For example, a bench mounted field tester was implemented for manual testing of HOT and EOT equipment on a preparation bench or even while in place on a train. The tester communicates with an HOT or EOT device to be tested and measures signals from the tested device to determine parameters such as center frequency, deviation, and relative signal strength. However, a correct interpretation of the measurement data to ascertain a valid pass/fail condition is very difficult. The signal strength indication is relative and requires a great deal of subjectivity in its interpretation, which is a non-trivial task even for an expert. Testing is currently limited to a point-to-point setup between the tester and the tested EOT/HOT device at a fixed distance. Other portable two-way field testers have also been developed to elicit operational data from EOT devices. Such field testers can communicate with and test only one EOT device at a time, and the testing still involves substantial manual reading and interpretation of measurement data. In summary, the existing approaches for EOT/HOT testing are ineffective, inefficient, and unreliable.
In view of the foregoing, it may be understood that there are significant problems and shortcomings associated with current testing techniques for the EOT and/or HOT devices.